1. Field of the Invention
The present invention relates to a copper alloy sheet that is suitable for electric/electronic components such as a connector, a lead frame, a relay, and a switch and that has excellent bending workability and stress relaxation resistance while maintaining high strength and good conductivity, a manufacturing method of the same, and an electric/electronic component using the same.
2. Description of the Related Art
Materials that are used in electric/electronic components as conductive components of a connector, a lead frame, a relay, a switch, and so on are required to have good conductivity in order to prevent Joule heat from being generated when electricity is supplied, and also is required to have high strength capable of resisting a stress given at the time of the assembly and operation of electric/electronic devices. Further, electric/electronic components such as a connector are required to have excellent bending workability since they are generally formed by bending after press punching,
Further, as electric/electronic components have recently come to be used more under a severe environment, a demand for their stress relaxation resistance is also becoming severer. For example, when they are used under an environment where they are exposed to high temperature as is the case with an in-vehicle connector, stress relaxation resistance is especially important. Stress relaxation is a kind of a creep phenomenon that a contact pressure of a spring portion of a material forming an electric/electronic component decreases with time under a relatively high-temperature environment (for example, 100° C.; to 200° C.) even though being kept constant at room temperature. That is, it is a phenomenon that, while a metal material is in a state of being given a stress, a dislocation moves due to the self-diffusion of atoms forming a matrix and the diffusion of solid solution atoms, and plastic deformation occurs to relax the given stress.
Especially in recent years, electric/electronic components such as a connector are on a trend toward smaller size and lighter weight, which has created an increasing demand for a thinner copper alloy sheet as a material such as a sheet having a thickness of 0.15 mm or less or further 0.10 mm or less. Therefore, strength level required of the material is becoming still severer. Concretely, strength level equivalent to 0.2% proof stress of 850 MPa or more, preferably 900 MPa or more, and still more preferably 950 MPa or more is desired.
Further, electric/electronic components such as a connector are on a trend for higher integration, higher-density mounting, and larger current, and accordingly, higher conductivity is more required of material sheets made of copper or a copper alloy. Concretely, conductivity level equivalent to 30% IACS or more, preferably 35% IACS or more is desired while 0.2% stress proof of 900 MPa or more is maintained.
High-strength copper alloys conventionally used include a Cu—Be based alloy (for example, C17200 (Cu-2 mass % Be)), a Cu—Ti based copper alloy (for example, C19900 (Cu-3.2 mass % Ti)), a Cu—Ni—Sn based copper alloy (for example, C72700 (Cu-9 mass % Ni-6 mass % Sit)).
However, in view of cost and environmental load, there is a tendency in recent years to avoid using a Cu—Be based alloy. Further, a Cu—Ti based copper alloy and a Cu—Ni—Sn based copper alloy have a modulated structure (spinodal structure) in which a solid solution element has a cyclic concentration fluctuation in a parent phase, and have a property of having low conductivity of about 10% to 15% IACS, though having high strength.
A Cu—Ni—Si based alloy has been drawing attention as a material relatively excellent in property balance between strength and conductivity. For example, a Cu—Ni—Si based copper alloy sheet can have 0.2% proof stress of 700 MPa or more while maintaining relatively high conductivity of about 30% to about 50% IACS by going through processes basically of solution heat treatment, cold rolling, aging, finish cold rolling, and low-temperature annealing. However, it is a general knowledge that in the Cu—Ni—Si based alloy sheet, it is difficult to achieve higher strength such as 0.2% proof stress of 900 MPa or more, for instance.
As a measure to achieve higher strength in the Cu—Ni—Si based copper alloy sheet, there has been known commonly used methods such as the addition of large amounts of Ni and Si and an increase in a rolling ratio of the finish rolling (thermal refining) after the aging.
However, though strength increases in accordance with the increase in the addition amounts of Ni and Si, when the amounts reach certain values, for example, when an amount of Ni reaches 3 mass % and an amount of Si reaches about 0.7 mass % or more, the increase in strength tends to saturate and it is difficult to achieve 0.2% proof stress of 900 MPa or more. Further, adding excessive amounts of Ni and Si is accompanied by deterioration in conductivity and tends to make an Ni—Si based precipitate coarser; so that bending workability is likely to deteriorate. The increase in the finish rolling ratio after the aging can improve strength but is accompanied by great deterioration in bending workability of the copper alloy sheet, especially in workability at the time of bending where a rolling direction is along a bend axis (what is called Bad Way bend).
Due to the above, there is some case where a sheet having strength level high enough to achieve, for example, 0.2% proof stress of 900 MPa or more cannot be worked into an electric/electronic component.
In recent years, with the intention of achieving higher strength of a Cu—Ni—Si based copper alloy sheet, Japanese Patent Application Laid-open No. 2007-169765, Japanese Patent Application Laid-open No. 2008-248333, Japanese Patent Application Laid-open No. 2009-007666, and so on, for instance, propose a copper alloy sheet to which a relatively large amount of Co (for example, 0.5 to 2.0 mass % Co or more) is added, that is, what is called a Cu—Ni—Co—Si based copper alloy. Further, with the intention of improving bending workability, Japanese Patent Application Laid-open No. 2008-106356, International Publication WO2009-123140, and so on, for instance, propose a copper alloy in which an amount of twins present (the number of twin boundaries included in crystal grains) is controlled.